Typically, gas turbine engines include a compressor for compressing air, a combustor for mixing the compressed air with fuel and igniting the mixture, and a turbine blade assembly for producing power. Combustors often operate at high temperatures that may exceed 2,500 degrees Fahrenheit. Typical turbine combustor configurations expose turbine vane and blade assemblies to these high temperatures. As a result, turbine vanes and blades must be made of materials capable of withstanding such high temperatures. In addition, turbine vanes and blades often contain cooling systems for prolonging the life of the vanes and blades and reducing the likelihood of failure as a result of excessive temperatures.
Typically, turbine airfoils are formed from an elongated portion forming an airfoil having one end configured to be coupled to a disc and an opposite end configured to be a tip. As shown in FIG. 1, the airfoil is ordinarily composed of a leading edge, a trailing edge, a suction side, and a pressure side. The inner aspects of most turbine airfoils typically contain an intricate maze of cooling circuits forming a cooling system. The cooling circuits in the airfoils receive air from the compressor of the turbine engine and pass the air through the airfoil. At least some of the air passing through these cooling circuits is exhausted through orifices in the leading edge, trailing edge, suction side, and pressure side of the airfoil.
The turbine airfoil walls are load bearing in which the cumulative centrifugal loading of the airfoil is carried radially inward via the outermost wall. As such, the thickness required at the tip of the airfoil determines the thickness at the root. Typical turbine airfoils have increasing cross-sectional areas moving from the tip to the root, as shown in FIG. 2. The tip thickness is determined by casting tolerances that include allowances for variation in wall thickness plus the potential for internal cores to shift during the casting process. While simply designing an appropriate tip thickness and increasing the tip thickness to the root is feasible for small turbine airfoils, such is not the case for large airfoils useful in large turbine engines. In particular, when this design is scaled up to the larger engines, the root becomes larger than can be accommodated. In addition, the larger sized airfoil requires a part span snubber or tip shroud for vibration control, both of which become very difficult with the large size and temperature. Thus, an alternative configuration for a turbine airfoil is needed that is capable of being scaled up in size to without encountering the limitations of conventional cast airfoils.